A cationic electrodeposition coating composition providing a corrosion-resistant coating to articles to be coated such as automobiles, etc. is an aqueous dispersion which is prepared by dispersing a cationic resin, a curing agent, and a pigment paste containing a pigment dispersed in a pigment dispersing resin, in an aqueous medium. The cationic electrodeposition coating composition is electrocoated on an article and then baked at a temperature of more than 160.degree. C. to cure the coated film on the article.
Recently, in order to reduce energy cost, it has been requested for the above cationic electrodeposition coating composition to be baked at a relatively low temperature (i.e. less than 160.degree. C.) for a short period of time. On the other hand, it is necessary that the cationic electrodeposition coating composition has pigment dispersion stability, as a matter of course. It is difficult to satisfy both these two performances in the prior art.
For example, when using a resin containing a quaternary ammonium salt as the cationic pigment dispersing resin, the resulting coating composition is superior in pigment dispersion stability, but corrosion resistance is not sufficient when baked at a low-temperature of 160.degree. C. or less.
It is also suggested that a tertiary sulfonium salt is used as the cationic pigment dispersing resin. When using this cationic pigment dispersing resin, the resulting coating composition is superior in corrosion resistance when baked at the low-temperature but is inferior in pigment dispersion stability, and stability of the paint bath is not sufficient.
Further, there is also suggested a pigment dispersing resin which contains a tertiary amine salt neutralized with acid, but it has the same disadvantage as that of the cationic pigment dispersing resin containing the above sulfonium salt.